Arrangement for eliminating disturbances in sound signaling



June 1929. w. HAHNEMANN El AL ARRANGEMENT FOR ELIMINATING DISTURBANCESIN SOUND SIGNALING Filed Feb. 4, 1921 2 Sheets-Sheet l June 1929. w.HAHNEMANN ET AL ARRANGEMENT FOR ELIMINATING DISTURBANCES IN SOUNDSIGNALING z Sheets-Shet 2 Filed Feb. 4, 1921 Patented June 4, 1929.

PATENT OFFICE.

WALTER HAHNEMANN AND LEONID ADELMANN, OF'KITZEIBERG NEAR KIEL, AND

HUGO LICHTE, OF KIEL, GERMANY, ASSIGNORS TO THE FIRM SIGNAL GESELL-SGHAF'I. M. B. H., OF KIEL, GERMANY.

ARRANGEMENT FOR IELI'JtIINA'II?ING' DISTURBANGES IN SOUND SIGNALING.

Application filed February 4, 1921, Serial No. 442,589, and in GermanyJanuary 25, 1917.

The devices used for the reception of sound signals usually comprise asound collecting or absorbing member, such as a diaphragm that respondsto sound vibrations, and a member that serves to receive the absorbedsound energy, such as a microphone. In such devices the latter membermay be associated with a v1- bratory body or structure, such as a tuningfork or the like.

Receiving apparatus of this kind are usually tuned as a. whole to thefrequency used for signaling. Although the tuning increases thesensitiveness of the receiver, it is accompanied by the disadvantagethat whenever the apparatus is excited by shocks, due to mechanical oracoustic disturbances, sounds are heard in the apparatus that correspondto the frequency for which the apparatus is tuned, so that its receivingfunction is seriously interfer-ed with. If the expedient of tuning isentirely dispensed with, or if the receiving apparatus as a whole istuned to a frequency that differs very much from the signalingfrequency, the sensitiveness of the apparatus to the sound signalsemployed will be considerably impaired.

The object of the invention is to provide a receiving apparatus of thiskind which is sufficiently sensitive to sounds whose rate of v1- brationcorresponds to the actual signaling frequency, but which is afiected bydisturbing sounds or noises to the smallest possible extent.

The invention relates more particularly to receiving apparatus whichcomprise a system consisting of two or more vibratory structures orbodies coupled to each other, and in which one of the structures ormembers of the system, which structure or member may consist of adiaphragm, a piston, the hull of a ship, or the like, assumes thefunction of collecting or taking in energy that arrives through thepropagating medium (water, air), while another member of the system thatacts as the receiver proper, and may take the form of a microphone or anelectromagnetic detector, assumes the function of converting the soundenergy into electrical energy that may be made erceptible by the humanear with the aid o an instrument such as a telephone receiver.

The invention consists in general in so tuning the various vibratorybodies or structures of which the apparatus is composed that after dueallowance is made for the .eifect produced on each vibratory body by itsbeing coupled to another, any one of the plurality of frequencies ofresonance which the composite vibratory apparatus will with thefrequency used or signaling, barring the particular frequency whichcorresponds to that of the vibratory receiving structure proper, i. e.that of the microphone or the like.

The purport of this will be explained by the following description withreference to the accompanying drawings in which Fig. 1 shows theresonance curves obtained from a diaphragm alone, a microphone alone andthe resultant curve when the diaphragm and microphone are coupledtogether;

Fig. 2 shows the resonance curve of a coupled system in which thediaphragm is more highly damped than the microphone;

Fig. 3 shows the resonance curve of a coupled system in which theresonance peak cor responding to the natural frequency of the diaphragmcoincides with the signaling frequency and the peak corresponding to thenatural frequency of the microphone is so far removed from the signalingfrequency as to have little effect on the functioning of the coupledsystem; and

Fig. 4 shows a sectional view of a practical example of a sound receiverconstructed ac cording to the invention.

If in a composite vibratory apparatus or system comprising two vibratorystructures coupled to each other, each individual structure has its ownfrequency of resonance, the behaviour of the system when subjected tovibrations will be such that each'of the individual vibratory structureswill exhibit two frequencies of resonance and these two frequencies willbe the same in each structure. One of them will, however, be lower andthe other higher than the frequencies of resonance of the individualstructures when separated from each other, and the effect produced ineach structure will be greatest at the particular frequency of resonancethat belongs to its own natural rate of vibration.

Hence in accordance with the invention, in receiving apparatuscomprising a collecting member that takes in the energy and an energytransferring or converting member, these vibratory members are so tunedand coupled as to bring about a coincidence between the particularpost-coupling frequency ossess, will coincide of resonance (i. e, thefrequenc fat which resonance is obtainedafter the ifierent vi-' bratorystructures are coupled to each other) that belongs to the natural rateof vibration of the collecting member and the frequency used forsignaling, but not between the signaling frequency and the post-couplingfrequency of resonance that corresponds to the natural rate of vibrationofthe said transferrin member. I

In ig. 1, in which the abscissa: designate the frequencies while theordinates designate the amplitudes, the solid graph represents a coupledvibratory structures are indicated by a broken line and a dash and dotline, the fre uency of resonance of the microphone by itse f lying at11. and that of the diaphragm by itself lying at n In accordance withthe invention N is the frequency that must beselected for signaling withthis'system. Disturbances which chiefly arise from shocks or vibrationsthat are practically non-periodic will be transformed in a system ofthis kind principally into periodical vibrations whose frequency is N,,so-

that signals with a-frequency of N will be clearly distinguishable fromthe disturbing noises. By coupling the two vibratory structures more orless closely the crests of the resonance curves may be shifted more orless apart. This can also be done by making the individual natural'ratesof vibration of the coupled vibratory structures of the system differfrom each other more or less widely.

It will be obvious that this expedient of altering the differencebetween'the post-cou pling frequencies of resonance is in itself a veryeffective means of eliminating disturbances. In accordance with theinventionthe freedom from disturbances can be considerably enhanced bydamping the vibrations of the diaphragm more than the vibrations of themicrophone' The resonance curve of a system damped in this way is shownin Fig. 2, in which the same signs of referenceare used as in Fig. 1.

Thus-in vibratory apparatus comprising a diaphragm coupled with amicrophone the post-coupling frequency of resonance of the diaphragm iscaused to coincide with the frequency of the sound used for signaling.This Is also done in an apparatus comprising a diaphragm, a specialvibratory structure and microphone contacts attached to the vibratorystructure. The post-coupling frequency of resonance of the microphone orof the vibratory structure withits attached microphone, may be madeeither higher or lower than the signaling frequency. In Figs. 1 and 2,the natural frequency. of the microphone, to-

ether with its corresponding post-coupling requency, are below' thenatural frequency of the'diaphragm and the corresponding postcouplingfrequency thereof used as the signaling frequency. But a preferredarrangement, particularly in cases of receiving apparatus in which thedetector used is a microphone, is one in which the natural note of themicrophone is so chosen that the post coupling frequency correspondingto it is higher thanthe signaling frequency.

' a For receivers consisting of a rigid casing,

a receiving diaphragm, and a microphone coupled to this latter, it is tobe considered as characteristic of the invention that the natural rateof the diaphragm is lower than that of the microphone, so that in thewhole apparatus the post-coupling frequency belonging to the diaphra mcoincides with the signaling frequency.- referably the vibratorystructures are so tuned that the natural period of the microphone liesabove the signaling frequency about twice the amount that the naturalperiod of the diaphragm lies above this frequency, (in practice 20% and40%). Then the coupling between the two parts is to be so chosen, forexample, by suitably distributing the masses over the two parts coupledtogether, that-the post-coupling frequency corresponding to thediaphragm coincides with the signaling frequency. In this way at thesame time, a degree of coupling especially advantageous for theefliciency o the receiver may be obtained.

Naturally, it is not absolutely necessary to make coincide with thesignaling frequency the post-coupling frequency belonging to thefundamental vibration of the diaphragm, but it is also possible tochoose a suitable harmonic of a diaphragm of an essentially lowerfundamental vibration.

In Fig. 3 of the accompanying drawings the most favourable relations oftuning for a receiver (casing with diaphragm and microphone) treatedaccording to the invention are represented by the resonance curves ofthe particular structures of the apparatus. The natural vibration of thediaphragm which, in this case, is identical with itsfundamental-vibration, is J, the natural vibration of the microphone isZ. By acoustically coupling these vibratory structures together thevibrations are displaced into J and Z re-- spectively, which are thefrequencies of resonance of the coupled system, J coinciding with thesignaling frequency 'X A special advantage obtained by this tuning isthat the inconstancy of the natural note of the microphone ceases to bea factor that greatly affects the efliciency of the receiver. I

Figure 4 presents a sectlonal view of a practical construction of asound receiver according to the principle previously explained. 1represents the casing to WhlCl'l the resonant diaphra m 2 is clamped bythe rivets 5, 5. Mounte on the diaphragm 2 and therefore acousticallycoupled with it 1s the microphone 3 in its usual form. The diaphragm 4of the microphone is coupled to the diaphragm 2 by means of the clamplngnut 7. The diaphragm 4 carries one electrode 8 while the casing 6carries the second electrode 9 between which electrodes are the carbongranules 10. The diaphragm 2 is tuned to the desired resonant frequencyby proper dimensions of size, thickness and material of the diaphragm.The microphone is also suitably tuned to the desired frequency asexplamed above.

In order to obviate the necessity of using a microphone, bi-resonant .ormulti-resonant electro-magnetic contrivances may be used which may bemade to act both as sending means or receiving means. In accordance withthe invention the frequency of the sound signals employed when receivingwith an arrangement of this kind would be one that does not belong tothe receiving device proper (energy-converter) In producingmulti-resonant apparatus of this kind each individual vibratory body orstructure is referably tuned by itself to a frequency of resonancewhich, when it is changed by the effect of the various coupledstrut'ures, results in the desired post-coupling frequency of resonance.This is done by using the degree of coupling that has been determined byexperiment or calculation to be the proper one. When once the amount bwhich the frequency of resonance is clzanged through the influence ofthe coupling has been ascertained in a trial apparatus, the preferableprocedure in tuning each indi-' vidual vibratory structure will be tosubstitute the amount of the mass of the cooperating parts to be coupledthereto, that affects its tuning, by attaching a weight of correspondingsize to it. In doing this it must be remembered that the vibratorystructure that takes in the sound energy from the propagating mediumupon which it abuts is also affected by a certain amountof the mass ofthis medium. In the cases of heavy mediumssuch as liquids this amount isconsiderable.

The term sound radiating member is used in the claims to definegenerically a member which takes up vibrations from or impartsvibrations to the sound propagating medium; while the termenergy-converting means is used to designate generically a device whichconvertssound energy into another form of energy, for example, intoelectrical energy, or Vlce versa.

We claim:

' 1. In sound signal apparatus, an individ' ually tuned vibratorystructure, and an individually tuned energ -converting means, means forcoupling said vibratory structure and said energy-converting meanstogether acousticallg, and the frequencies of resonance of t e coupledsystem being such that the resonance frequency corresponding to theenergy-converting means is substantially different from the sound signalfrequenc 2. In sound signal apparatus, an in ivid' ually tuned soundradiating member, and an individually tuned energy-converting means,means for coupling said sound radiating member and saidenergy-converting means together acoustically, and the fre uencies ofresonance of the coupled system eing such that the resonance frequencycorresponding to the energy-converting means is substantially differentfrom the sound signal frequency- 3. In sound signal apparatus, anindividually tuned vibratory structure, and an individually tunedmicrophone, means for coupling said vibratory structure and saidmicrophone together acoustically, and the frequencies of resonance ofthe coupled system being such that the resonance frequenc correspondingto the microphone is substantially different from the sound signalfrequency.

4. In sound signal apparatus, an individually tuned vibratory structure,and an individually tuned energy-converting means, means for couplingsaid vibratory structure and said energy-converting means togetheracoustically, and the frequencies of resonance of the coupled systembeing such that the resonance frequency corresponding to theenergy-converting means is substantially higher than the sound signalfrequency.

5. In sound signal apparatus, an individually tuned vibratory structure,and an individually tuned energy-converting means, means for couplingsaid vibratory structure and said energy converting means togetheracoustically, and the frequencies of resonance of the coupled systembeing such that the resonance frequency corresponding to theenergy-converting means is substantially different from the sound signalfrequency while the resonance frequency corresponding to the vibratorvstructure substantially coincides with the sound signal frequency.

6. In sound signal apparatus, an individually tuned vibratory structure,and an individually tuned energy-converting means, means for couplingsaid vibratory structure and said energy-converting means togetheracoustically, the frequencies of resonance of the coupled system beingsuch that the resonance frequency corresponding to theenergy-convertingmeans is substantially different from the sound signalfrequency, and

comprising. a tuned sound radiatin phragm, means for coupling said diapragm greater; vertin f 7. ulti-resonant the darn of thevibratory-structure being anthdi damping o the energy-consound signalapparatus,

dia-

toa tuned sound detector, the tunings and coupling bein such that thefrequency of resonance of t e coupled system corresponding to the saidsound detector is substan-' tially difierent from the sound signal frekquency.

- 8. Multi-resonant sound signal apparatus, comprising a tuned soundradiatin diaphragm, means for coupling said dlap ragm 'to a'tuned sounddetector, the tunings and the couplin being such that the frequency ofresonance 0 the coupled system corresgondstanin to the said sounddetector is su tia y different from the soundsignal frequency and thatthe frequency of resonance of the coupled system corresponding to theabout twice as great as the said diaphragm substantially coincides withthe sound signal frequency. f

9. In sound signal apparatus, a vibratory structure indivi ually tunedto certain frequency higher than the sound signal fre-' quenc anenergy-converting means indiferent from the sound si 'nal frequency.

In testimony whereof we afiix our signatures.

- LEONID ADEL'MANN.

WALTER HAHN EMANN. HUGO LIGHTE.

ifierence be .vidua y tuned to a frequency higher than ed'system'corresponding to the energy-converting means is substantiallydi15- 7

